1. Field of the Invention
The present invention concerns an inductive/MR composite type thin-film magnetic head which is integrally equipped with an inductive head used for writing and a magnetic resistance (MR) head used for readout, and which can be used in recording and playback devices of various types of equipment such as computers and word processors, etc., for example, in hard disk drives, etc.
2. Background Information
Recently, composite type thin-film magnetic heads in which an inductive head used for writing and an MR head used for read-out are combined into an integral unit have been employed as thin-film magnetic heads used in magnetic disk drives of computers, etc. In such composite type thin-film magnetic heads, the MR head has a large playback sensitivity and the playback output is not dependent on the relative speed with the recording medium. Accordingly, it is possible to reduce the track width and to reduce the number of turns of the coil so that the impedance is lowered, thus making it possible to achieve higher-density magnetic recording, a more compact apparatus and an increased output.
In conventional composite thin-film magnetic heads, as is shown for example in FIGS. 8 and 9, an MR head 5 consisting of an MR element 4 which is sandwiched between a lower shield 2 and upper shield 3 is formed on the surface of a ceramic substrate 1 which is covered by an insulating underlayer film. An inductive head 11 is then formed on top of this by using the aforementioned upper shield 3 as a lower magnetic film, and laminating a magnetic gap film 6, organic insulating layers 7 and 8, conductive coil 9 and upper magnetic film 10 on top of said lower magnetic film. The conductive coil 9 is generally formed in a spiral shape centered on the back gap 12 by means of a conductive material plating formed using a photolithographic technique.
The recording of signals on a recording medium 13 is accomplished by applying a square-wave writing current of the type shown in FIG. 10A to the coil 9 via lead wires 14 and 15 so that magnetic flux is generated in the magnetic transducing gap 16 between the upper and lower pole parts at the tip ends of the aforementioned magnetic films, thus creating regions of inverted magnetization known as magnetization transitions with the timing of the plus-minus switching of the writing current. The recorded signals are reproduced with high fidelity as follows: i.e., the magnetic flux from the recording medium passing through the MR element 4 varies with the timing at which the abovementioned magnetization transitions pass between the aforementioned upper and lower shields, and this variation causes a variation in the resistance of the MR element, so that electrical signals are produced.
A writing head with a superior recording capacity is necessary in order to realize high-speed, high-density recording in such a composite type thin-film magnetic head. However, in cases where signals are recorded at a high density on a recording medium, adjacent magnetization transitions interfere with each other so that a nonlinear shift in the writing positions known as a nonlinear transition shift (NLTS) occurs in the recording medium. This increases the read-out error during the playback of the signals.
The conventional inductive head shown in FIGS. 7 and 8 has a resistance and inductance which correspond to the coil length of the spiral-form coil 10. Here, the inductance has a positive correlation with the area surrounded by the outermost circumference of the aforementioned coil. Furthermore, because of the effects of magnetic bodies such as the upper magnetic film 10 and upper shield 3, etc., present in the surrounding area, the inductance is larger than it would be in the case of the coil alone. When the resistance and inductance of the aforementioned coil are increased, the impedance increases. Accordingly, a delay component created by this impedance is generated in the writing current that flows through the coil.
If this delay is large, as is shown in FIG. 10B, a distortion known as "corruption" is generated in the square waveform of the writing current, so that the time required for plus and minus switching of the writing current, i.e., the rise time, is increased. If the rise time of the writing current is large, the time required for the inversion of the direction of the magnetic flux generated in the magnetic transducing gap, i.e., the rise time of the magnetic flux, is increased. Since a positive correlation of the type shown in FIG. 11 exists between the rise time of the magnetic flux and the abovementioned NLTS, it is important to lower the inductance of the aforementioned coil, and thus reduce the rise time of the writing current, in order to reduce the NLTS.
Furthermore, an eddy current loss caused by the writing current flowing through the coil is generated in the yoke parts of the upper and lower magnetic films, and this eddy current loss generates a delay in the high-frequency component of the magnetic field generated between the upper and lower pole parts. Accordingly, if the eddy current loss in both of the aforementioned magnetic films can be reduced, the rise time of the magnetic flux can similarly be shortened so that the NLTS can be reduced. The eddy current loss in the aforementioned magnetic films can be reduced by shortening the yoke length, i.e., the magnetic path length L'. However, in order to do this, it is necessary to reduce the pitch per turn of the coil.
In the case of conventional spiral-form coils formed by the abovementioned photolithographic technique, however, there is an upper limit on the aspect ratio from the standpoint of manufacturing technology. As a result, the thickness of the coil is limited in cases where the coil pitch is reduced. Accordingly, the coil resistance has an inversely proportional relationship with the magnetic path length, as indicated by the broken line in FIG. 4 Meanwhile, because of restrictions in terms of the electrical circuit formed by the aforementioned lead wires and coil, etc., the coil resistance cannot be increased beyond a certain upper-limit value. As a result, the minimum value of the magnetic path length, i.e., the yoke length of the aforementioned magnetic films, is determined by the set value of the coil resistance. Accordingly, there are limits to the reduction in NLTS that can be achieved by reducing the eddy current loss of the upper and lower magnetic films.
Thus, it is desired to provide an inductive/MR composite type thin-film magnetic head which makes it possible to reduce NLTS and prevent the generation of read-out error while realizing high-speed, high-density recording. Furthermore, it is desired to provide an inductive/MR composite type thin-film magnetic head which can be manufactured relatively easily and inexpensively using conventional manufacturing techniques "as is."